General morphology and organelle microtopography in prepubertal (a) and adult (b) ovine cumulus-oocyte-complexes (COCs) after 24 hours of IVM. a) Representative TEM micrograph showing expanded cumulus cells (CC), a zona pellucida (ZP) devoid of CC prolongations and a roundish oolemma. Bar: 2 μm. Inset in a): representative LM image showing CC expansion after detachment from the ZP. Bar: 20 μm. b) Representative TEM micrograph showing several mitochondrial clusters (m), electron-lucent vacuoles (Va) and electron-dense lipid droplets (LD). Bar: 2 μm. Inset in b): representative LM image of a round oocyte, provided with a continuous perivitelline space (PVS) and surrounded by a compact zona pellucida (ZP). Bar: 20 μm.